Croatia has rejected an Israeli decision to call off a deal for Zagreb to purchase F-16 fighter jets after months of stalling due to a lack of US approval. Croatia had in March agreed to buy 12 used F-16s from Israel to replace its Russian-made MiG-21s. The deal, worth $500 million (440 million euros), was the Balkan nations biggest arms purchase since splitting from former Yugoslavia in the 1990s war. But Washington objected to the sale of the US-made jets because it wants the removal of electronic system upgrades that Israel added in a rare defense dispute between the close allies. After months of delay, the Croatian defense ministry said Thursday it asked Israel for "official information by January 11 on whether Israel can deliver the planes." If Croatia is not able to buy the specific jets it chose, the government will cancel the deal, the ministry said. "We are not happy that this happened," said Croatian Prime Minister Andrej Plenkovic on Wednesday. "The government firmly stands by its decision ... to realize only the offer as accepted" in March, he said. Israeli Prime Minister Benjamin Netanyahu has tried in vain to convince the former Pentagon chief, Jim Mattis, to limit the US conditions on the sale of the jets. He has also sought to convince US Secretary of State Mike Pompeo to agree on the sale of the F-16s, yet the top diplomat has rejected Netanyahu’s request.